The ability of a complex organism to produce organs through specific and stereotyped patterns of cell division is fundamental to its development. How plants and animals specific proper cell division patterns in organogenesis is poorly understood. The high plant Arabidopsis thaliana provides an excellent system in which to study the control of cell division as it relates to a developmentally complex organism, since plant meristems provide a defined structure in which the numbers and patterns of cell division are tightly controlled. To provide a better understanding of this fundamental histological problem, the following proposal describes experiments which are designed to define the role of the WIGGUM gene in the control of cellular proliferation in shoot and floral meristems. The phenotype of wiggum mutants suggests that WIGGUM acts to restrict cell division, either in the peripheral zone of shoot and floral meristems or in the epidermal and/or subepidermal cell layers of these meristems. Thus, the proposed experiments are designed to test these two hypothesis to determine the mechanism by which WIGGUM controls meristem size. Furthermore, experiments are proposed to expose potential interactions between WIGGUM and other meristem genes to define the meristem control pathways. The proposed basic research studying mechanisms of cell division control as it relates to organogenesis is a vital foundation from which more applied, health-related research will greatly benefit.